Referring to FIGS. 1 and 2, a conventional mattress 50 generally has a layer of pocket coil springs 57, alternatively know as Marshall Type Springs, engaged with a base 52. Mattress 50 further has cushion layers 53 and 54 disposed above pocket coil springs 57 and a mattress ticking cover 51. First described in U.S. Pat. No. 685,160, a Marshall Type Spring is a coil spring 56 encased in a material pocket 55. The pocket coil assemblies are made by inserting coil springs 56 into respective fabric coil pockets 55 that are usually strung together as a continuous pocket coil strip.
U.S. Pat. No. 2,236,007 discloses a Marshall Type Spring having fiber stuffing added into the core of the pocket coil spring to help absorb forces placed upon the actual pocket coil spring by absorbing some of those forces in the fiber filling material.
U.S. Pat. No. 8,266,745 discloses a Marshall Type Spring employing a fill material, including foam or fiber, residing in the pocket with the spring coil, to reduce and eliminate noise and prevent the fabric that surrounds the spring from getting sucked inside the pocket when a person gets onto or off of the bed.
What most pocket coil mattresses have in common is that the coil spring, contained in an individual fabric pocket, lies under a sheet or multiple sheets, of padding and cushioning material that provide initial loading softness, a softer sleeper feel, help in reducing localized high pressure interface points, reduce the sensation of lying directly on a metal spring, and help conform to body contours. Mattresses of this type are often flipped at some time interval to help mitigate and eliminate the problems associated with getting body imprints in one or more of the cushioning layers from the sleeper repeatedly lying in a similar position night after night.
Referring to FIG. 3, another shortcoming of having a single or multiple sheets of cushioning material 53 above a layer of pocket coils 58 is that compressive forces caused by the weight of a body 49 (“sleeper compressive forces”) are transmitted in the plane of cushioning material 53, a plane that is generally at right angles and perpendicular to the vertical plane of the pocket coil unit. This results in the sleeper compressive forces being transferred laterally to adjacent pocket coils even though those same coils might not be subjected to direct sleeper forces. This creates an indentation well 60 that causes the sleeper to be drawn into the core of mattress 50 rendering mattress 50 uncomfortable for sleeping.
An additional problem of the indentation well effect occurs for a second sleeper utilizing the same mattress at the same time as the primary sleeper. The second sleeper can often be subjected to the indentation well effect of the primary sleeper and be subjected to forces that draw that sleeper into the same sleep space as the primary sleeper. Obviously, the inverse is also true and the primary sleeper can be drawn into the indentation well effect created by the secondary sleeper. Both of these situations result in a situation in which neither sleeper is able to get comfortable in his or her own space due to shortcomings in the way that sheet cushioning material behaves in a current mattress configuration.
A further shortcoming of the sheet cushioning above the pocket coil is that the sheet cushioning material takes on a trampoline effect when loaded from above. Rather than just acting as a cushioning material to provide initial loading softness, a softer sleeper feel, help in reducing localized high pressure interface points, and help in conforming to body contours, the sheet cushioning is often additionally acting like a trampoline and exhibiting its own spring effect. The magnitude of the trampoline effect usually correlates closely with the tensile strength of the cushioning material. The cushioning material is being held in place above pocket coil springs that are not being compressed and is resisting downward defection in areas that are being subjected to compressive forces due to the lateral, in plane, tensile strength of the material. In essence, the sheet cushioning material is acting like a spring unit in its own right due to the tensile strength trampoline effect. This effect is often at odds with the desire of the cushioning material to provide an initial softness to the sleeper. Concerning hospital and nursing home mattresses, a significant problem concerns patients developing decubitus ulcers from increased mattress interface pressures. A goal of the sheet cushioning above a pocket coil core in a hospital mattress is to reduce decubitus ulcer formation by reducing localized high patient interface pressures. However, the trampoline effect exerted by the sheet cushioning layers above the coil unit works to adversely impact this goal.
An added deficiency associated with sheet cushioning above the pocket coil concerns delivery of the mattress. It is well known within the industry that mattresses are normally shipped in a flat configuration in either a horizontal or vertical orientation. Bending the mattress during initial delivery and setup often results in mattresses being damaged and returned. Often the failure mechanism within the mattress is the result of the sheering, permanent dislodging, or deformation of the sheet cushioning material. Furthermore, the need to ship mattress in a flat orientation adds to both the expense and logistics involved in mattress shipping. Often it requires two men and a truck to deliver a mattress to a consumer. It would be inherently advantageous to be able to roll up and compress mattresses for shipping and eliminate the costs associated with shipping a flat mattress. Additionally, the cost of storage in terms of floor space for both the manufacturer and retailer would be greatly reduced if the mattress could be stored in a rolled up and compressed format.
An existing problem when sleeping on different sheeted cushioning materials, especially different types of foam including, but not limited to, polyurethane, latex, and memory foam, is that they have a tendency to cause the sleeper to feel uncomfortably warm or hot when lying on the mattress. This is partially due to the fact that many of these sheeted cushioning materials have insulating properties that restrict body cooling for those sleeper's body parts that are in direct contact with the mattress. Couple this property with the very nature of a sheet of cushioning material's inhibition of airflow through or around the cushioning material makes the cooling problem worse. The inability of a sleeper to properly regulate their temperature, coupled with the fact that a sleeper's wake-up mechanism is partially triggered via internal temperature regulation, can make the inclusion of sheeted cushioning materials in pocket coil mattresses a significant factor in poor sleep quality associated with the mattress.
One of the major causes of mattress failure is a degradation of the sheet cushioning materials. This is a direct result of fatigue softening that is particularly dominant in sheet foam cushioning materials that are subjected to shear loads consistent with sleeper forces exerted on the mattress. Over time and successive loading, the foam starts to lose its ability to resist compression. This degradation of the sheet cushioning materials has led mattress manufacturers to recommend flipping the mattress to mitigate and delay this degradation.
The sheet cushioning also acts to trap dust, dust mites, and potentially other microorganisms. Over an extended period of time this can become a serious health hazard, especially to those individuals who are highly allergic or immunosuppressed. Additionally, hospitals and nursing homes mitigate this problem by covering the mattresses with barrier fabrics.